Automatic exposure time control for cameras

ABSTRACT

A camera capable of automatically determining exposure time. The camera includes an external photosensitive element for receiving light which is external to the camera objective and an internal photosensitive element for receiving light which has passed through the objective internally thereof. A relatively simple electrical control structure is actuated by the external photosensitive element to determine the exposure time. Simultaneously, a compensating signal is derived from the internal photosensitive element to compensate for inaccuracies inherent in the exposure time determination which would result from the influence of the external photosensitive element along.

finite States Keisha, Tokyo-to, Japan [22] Filed: Feb. 16, 1970 [21]Appl. No.: 11,405

[30] Foreign Application Priority Data Feb. 24, 1969 Japan .44/13182[52] US. Cl ..95/10 CT, 95/42, 95/43 EB [51 Int. Cl. ..G03b 7/08, G03b9/62 [58] Field of Search ..95/10 C, 53 E, 53 R, 42

[56] References Cited UNITED STATES PATENTS 3,232,192 2/1966 Stimson..95/10 C 3,349,678 10/1967 Minoru Suzuici et a1 ..95/ 10 C 3,397,6298/1968 Tadamichi Mori et al ..95/10 C Nolousawa 51 Aug.15,1972

[ AUTOMATIC ES Tim 3,418,479 12/1968 Schmitt ..95/1OC CQNTROL FOR CRAS3,473,453 10/1969 Gross ..95/10C I Egg- New, 31323132,; 111323$523523??? ja /75%? [73] Assignee: Asahi Kogaku kogyo Kabushiki PrimaryExaminer-Joseph F. Peters, Jr. Attorney-Steinberg & Blake 5 7] ABSTRACTA camera capable of automatically determining exposure time. The cameraincludes an external photosensitive element for receiving light which isexternal to the camera objective and an internal photosensitive elementfor receiving light which has passed through the objective internallythereof. A relatively simple electrical control structure is actuated bythe external photosensitive element to determine the exposure time.Simultaneously, a compensating signal is derived from the internalphotosensitive element to compensate for inaccuracies inherent in theexposure time determination which would result from the influence of theexternal photosensitive element along.

11 Claims, 10 Drawing Figures PATENTEDAUB 1 I912 3.683; 766

INVENTOR KU M o NMSU AWA BYyi- ATTORNEYS PATENTEDAUS 1 5 m2 sum 2 OF 4mvsmon 7; UK um u Amsumm 124,4, ATTO NEYS PATENTEDMIB15 I912 3.683. 766

SHEET [1F 4 INVENTOR 3 0mm News Wr ATTORNEY$ AUTOMATIC EXPOSURE TIMECONTROL FOR CAMERAS BACKGROUND OF THE INVENTION determine automaticallya factor such as the proper exposure time.

Cameras of this latter general type are well known and are considered tobe highly desirable because the light which is received by the internalphotosensitive element has passed through the objective and isconsequently the same light which is received by the film when thelatter is exposed, so that in this way an extremely high degree ofaccuracy can be achieved in the automatic exposure determination.

Of course it is also possible to determine the exposure by way of aphotosensitive element which receives light which is external to theobjective.

It is well known that these two types of light-respom sive structureshave their own advantages and disadvantages, so that quite often it isdifficult for the designer to determine whether one or the other shouldbe used. Thus, in the case of the photosensitive element which receiveslight externally of the objective, there is an inherent inaccuracy inthat the image angle is different from and does not coincide with theimage angle through the objective used for actual exposure of the film.As a result it is unavoidable that there will be a light measurementerror, which may be of considerable significance when using a camerahaving interchangeable objectives with different image angles. This isthe case in a single lens reflex camera.

On the other hand, the internal photosensitive element which receiveslight whichhas already passed through the objective is capable ofproviding a far more accurate measurement of the light so that anylightmeasurement errors due to non-coincidence of the image angles ofthe objective and the light-receiving element are eliminated. Thus, withthis latter type of construction it is unnecessary to design an externalphotosensitive element so that it will operate properly with only onegiven objective and will unavoidably have inaccuracies with otherobjectives. However, the internal photosensitive element had thedisadvantage of necessitating a construction and control which are farmore complex than those necessitated by the external photosensitive typeof element. With the internal photosensitive element it becomesnecessary to provide a far more complex electrical circuit for exposurecontrol as determined by the light measurement, and particularly in thecase of a single lens reflex camera it is often necessary to provide adevice for temporarily storing or memorizing the extent of illuminationof the object from an instant immediately before the shutter is releaseduntil the shutter operation is completed.

In this latter connection, it is to be noted that in a single lensreflex camera where there is an internal measurement of light which haspassed through the objective, this light is reflected by the tiltablemirror toward the viewfinder so that it will not reach the film, and itis this light which is reflected by the mirror which is measuredinternally. As a consequence, immediately subsequent to tilting up ofthe mirror in order to make the exposure with opening of the shutter,the mirror becomes displaced to a location beyond the path of lightpassing through the objective, and thus it is not possible with thistype of construction to continue to measure the light once the mirrorhas been tilted out of the path of light entering the objective. Theresult is that there is an interruption in the measurement of the light,this interruption lasting for the interval required for the mirror totilt upwardly and for the film to be exposed. It is therefore essentialwith cameras of this latter type to provide circuitry capable ofmemorizing the information pertaining to the intensity of the light atthe object which is to be photographed, and this memorized informationis then used to control the exposure time. For example, it is known touse in structures of this latter type memory capacitors which areinitially charged, before the mirror is tiled upwardly, to an extentdetermined by the intensity of the light at the object to bephotographed, and this requirement of a memory capacitor with theadditional electrical components and circuitry required to charge thememory capacitor according to the light intensity and to take from thememory capacitor the stored charge so as to expose the film properlycreates the above necessity for the complex electrical circuitry used inconnection with storing or memorizing the extent of illumination of theobject, in the case of a single lens reflex camera. These problems arenot present with an external photosensitive element. The externalphotosensitive element can continuously receive the light, up to theinstant of and during the actual exposure of the film, so that all ofthe above problems inherent in the use of measurement of lightinternally in a single lens reflex camera are eliminated with the use ofthe external photosensitive element.

Summing up, the situation is that with a external photosensitive elementit is possible to maintain the entire construction far simpler and lessexpensive than a camera having an internal photosensitive element, butthis is done at the price of sacrificing accuracy particularly in thecase of interchangeable objectives. On the other hand, while a highdegree of accuracy can indeed be maintained with the internalphotosensitive element which receives light which has passed through theobjective, this latter type of element necessitates a far more expensiveand complex construction, so that the costs are unavoidably increasedwith this type of construction.

SUMMARY OF THE INVENTION It is accordingly a primary object of thepresent invention to provide a camera with a construction which takesadvantage of both of the above-types of photosensitive elements.

Thus, it is a more particular object of the present invention to providea camera capable of utilizing the simplicity of structure which resultsfrom the use of an external photosensitive element while at the sametime maintaining the accuracy which results from the use of an internalphotosensitive element.

Furthermore, it is an object of the present invention to provide acamera which can automatically determine exposure time not only inaccordance with light received by internal and external photosensitiveelements but also according to other exposure-determining factors suchas the particular speed of the film which is to be exposed and theparticular exposure aperture which results from the setting of thediaphragm.

It is also an object of the present invention to provide a camera withconstruction capable of achieving these objects without requiring theoperator to learn a type of camera operation different from that whichis conventionally used and while at the same time maintaining the entireorganization simple, compact, and relatively inexpensive without anysacrifice in accuracy.

According to the invention an external photosensitive means is providedfor receiving light which is external to the camera objective. Anelectrical means is operatively connected with this externalphotosensitive means to be actuated thereby for determining the exposuretime in accordance with the light which is received by this externalphotosensitive means. An internal photosensitive means is provided forreceiving internal light which has passed through the interior of theobjective. This internal photosensitive means is operatively connectedwith the electrical means to provide for the latter a compensatingsignal which will compensate for inaccuracies inherent in determinationof the exposure time solely by the external photosensitive means. As aresult it becomes possible to achieve the accuracy inherent in the useof an internal photosensitive means while maintaining the low costsinherent in the simplicity of the structure resulting from the use of anexternal photosensitive means.

BRIEF DESCRIPTION OF DRAWINGS The invention is illustrated by way ofexample in the accompanying drawings which form part of this applicationand in which:

FIG. 1 is a diagrammatic representation of an electrical means anda pairof photosensitive means of the invention;

FIG. 2 is a diagrammatic representation of another embodiment of thestructure of the invention;

FIG. 3 is a further diagrammatic representation of an electrical meansand a pair of photosensitive means of the invention, as used todetermine automatically the exposure time;

FIG. 4 illustrates yet a further variation of the electrical means;

FIGS. 5 and 6 respectively illustrate still further embodiments ofstructures according to the invention;

FIG. 7 is a fragmentary sectional diagrammatic representation of themanner in which the pair of photosensitive means are arranged, FIG. 7also illustrating schematically how parts of the electrical means areactuated when the shutter is actuated; and

FIGS. 8-10 are respectively schematic front elevations of camerasprovided with controls of the type illustrated in FIGS. 2, 5, and 6.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring first to FIG. 1, thestructure illustrated therein includes an internal photosensitive means1 shown at the upper left portion of FIG. 1, taking the form, forexample, of a photosensitive resistor situated within a camera in thepath of light which has passed through the objective. Thus, referring toFIG. 7 it will be seen that there is diagrammatically illustratedtherein a camera housing 30 provided with an objective 32. Light whichtravels along the optical axis 34 is received by the photosensitivemeans 1 which is positioned in the mannerv schematically illustrated inFIG. 7. In the case of a single lens reflex camera this is the lightwhich is directed up through the viewfinder before the exposure is made,and of course it is this very same light which is used to expose thefilm. The electrical means of the invention includes in the embodimentof FIG. 1 all of the structure illustrated therein with the exception ofthe internal photosensitive means I and the external photosensitivemeans 4. This external photosensitive means also takes the form of aphotosensitive resistor, for example. It is situated, for example, inthe manner shown schematically in FIG. 7, behind a window 36 formed inthe front wall of the camera housing 30, so that light traveling alongthe axis 38, externally of the objective 32, will be received by thephotosensitive resistor 4.

The electrical means shown in FIG. 1 includes an adjustable resistor 2connected in series with the photosensitive means 1 and capable of beingadjusted to a given value. This resistor 2 is connected in series withthe battery 3.

The external photosensitive means 4 is connected to a control switch 5which normally has a closed position engaging the contact a. This switch5 is also shown in FIG. 7. Thus, as may be seen from FIG. 7 there is adiagrammatic representation of a spring urging the switch 5 to itsnormal position engaging the contact a.

Through this normal position of the control switch 5, the photosensitivemeans 4 is connected in series with a second adjustable resistor 6 whichis preset to provide for the electrical means a resistance to achievethe required accurate results.

The electrical means further includes a capacitor 7 which operates tomeasure the difference between the light received by the pair ofphotosensitive means 1 and 4, and this capacitor 7- will memorize orstore this differential at least temporarily so as to provide in thisway a compensating signal as determined by the difference between thelight received by the pair of photosensitive means 1 and 4.

This capacitor 7 is controlled by way of a capacitor switch means 8which normally has the position engaging the pair of contacts X and Y sothat in the normal position of the switch means 8 the capacitor 7 isconnected between the internal photosensitive means 1 and the externalphotosensitive means 4 not only through the switch means 8 but alsothrough the control switch means 5 which normally engages the contact a.The switch means 8 forms a double-throw switch capable of connecting thecapacitor 7 to the other pair of contacts X and Y The contact X isconnected electrically with the negative pole of the battery 3 while thecontact Y is connected to the base of a high-input impedience,current-control transistor means 11. The electrical means furtherincludes a timing capacitor 9 which is connected electrically with theexternal photosensitive means 4 when the control switch means 5 isswitched over to its other position engaging the contact b. At this timethe timing capacitor 9 will be connected in series between thephotosensitive means 4 and the battery 3.

The electrical means also includes a triggertransistor means connectedinto the circuit so that the voltage across a timing capacitor 9 isapplied to the control pole thereof, while the emitter of the transistor11) has applied thereto a bleeder voltage of the battery 3 determined bythe output terminal of the amplifying transistor 11 and thepotentiometer 12 which can be adjusted according to the speed of thefilm which is exposed in the camera. Thus, the variable resistor formedby the potentiometer 12 is capable of introducing into the controls theexposure-determining factor of the film speed.

The junction between the collector of the triggertransistor means 10 andthe collector resistor 13 is electrically connected with a switchingtransistor means 14. In the current supply circuit of the battery 3, andunder control of the switching transistor 14, there is theseries-connected electromagnetic means 16 which maintains the shutteropen as long as this electromagnetic means 16 is energized. A mainswitch 17 is provided for closing or opening the entire circuit and iscommon to all of the current supply circuits of the battery 3.

Referring to FIG. 7, there is diagrammatically illustrated therein ashutter-actuating means in the form of a plunger 40 which is depressedin opposition to the spring 42 by the operator when it is desired tomake an exposure. In order to make an exposure the bottom end of theplunger 40 will engage the tripping lever 42 or the like of a camerashutter 44 which may, for example, be a focal plane shutter in the caseof a single lens reflex camera. Once the shutter has been tripped so asto expose the film it is maintained open by the electromagnetic means 16and automatically closes when the electromagnetic means 16 becomesunenergized.

As may be seen from FIG. 7, during the initial part of the movement ofthe shutter-actuating means 40, a projection 46 thereof will engage thedouble-throw switch 8 so as to move the latter from its normal positionshown in FIG. 7 engaging the contacts X, and Y, to its other positionengaging the contacts X Y The left end of the arm of the switch 8 has,for example, a roller engaging the right surface of the cam 46 so thatthe switch will be maintained at the contacts X Y during continueddepression of the plunger 40 by the operator.

As the shutter-actuating means 40 continues to move downwardly, asviewed in FIG. 7, a second cam 48 thereof will engage the switch 5 so asto displace the latter from its normal position engaging the contact ato its other position engaging the contact I). This engaging of thecontact bby the switch 5 takes place simultaneously with the tripping ofthe shutter 44 by the shutteractuating means 40.

In FIGS. 2-6 the components which perform the same functions as those ofFIG. 1 are designated by the same reference characters.

Thus, referring to FIG. 2, in this embodiment an adjustable means 18 isdiagrammatically shown in front of the external photosensitive means 4.This adjustable means takes the form of a diaphragm 18, and thisadjustable diaphragm 18 is also diagrammatically illustrated in FIG. 8.It is capable of being manipulated by the operator so as to introduce apredetermined value of an exposure-determining factor by influencing theamount of light which is received by the external photosensitive means4. Thus, by way of this diaphragm 18 it is possible to introduce thefactor of the speed of the film which is exposed or the size of theexposure aperture.

As is diagrammatically illustrated in FIG. 2, the variable resistor 2takes the form of a potentiometer mechanically coupled with thediaphragm 18 so as to be adjusted simultaneously with the latter.

Thus, the potentiometer 2' of FIG. 2, which is connected in series withthe internal photosensitive means I, will be automatically adjusted whenthe diaphragm 18 is adjusted so as to adjust the electrical means inaccordance with the setting of the diaphragm 18.

FIG. 2 shows a fixed resistor 12' forming the emitter resistor of thetrigger-transistor means 10. However, this resistor 12 may be replacedby a variable resistor in the form of a potentiometer or the like, forexample, in the event that it is desired to introduce in this way intothe circuit an exposure-determining factor as is the case with thepotentiometer 12 of FIG. 1. This factor will be that one which is notintroduced by the diaphragm 18. Thus, if the diaphragm 18 of FIG. 2 isused to introduce the size of the exposure aperture, the variableresistor 12 will be used to introduce the film speed, while if thediaphragm 18 is used to introduce the film speed the variable resistor12 would be used to introduce the size of the exposure aperture.

In the embodiment of the invention which is illustrated in FIG. 3, thecurrent-controlling transistor means 11 is positioned in the electricalmeans between the external photosensitive means 4 and the timingcapacitor 9.

With the arrangement of FIG. 4, the current-controlling transistor means1 1 is connected directly to the battery 3 and is in series with anelectric meter 19, which is mechanically coupled with the adjustablemeans 18 which takes the form of a diaphragm, as pointed out above. Thismeter 19 has a moving coil, for example, which turns to actuate amechanical transmission which will automatically adjust the diaphragm18.

FIGS. 5 and 6 illustrate further embodiments of the invention. In bothof these embodiments the variable resistor 2' is connected in serieswith the internal photosensitive means 1 and is automatically adjustedupon adjustment of the diaphragm 20 to determine the exposure aperture.This diaphragm 20 is situated at the objective 32 as schematicallyillustrated in FIGS. 9 and 10. Thus, the amount of light which isreceived by the internal photosensitive means 1 is adjustedsimultaneously with the variable resistor 2. In FIGS. 5 and 6 there isalso a diaphragm 18 situated in the path of the light which reaches theexternal photosensitive means 4. In FIGS. 5 and 6 this diaphragm 18 ismechanically coupled with the variable resistor 6' so as to adjust thecircuit according to the setting of the diaphragm 18. This resistor 6'is of course in series with the photosensitive means 4 when the switch 5is in its normal position engaging the contact a. The diaphragm 18 isseparate from the diaphragm 20 in the case of FIG. 6, as isschematically illustrated in FIG. 10. However, in the case of FIG. 5,the diaphragms 18 and 20 are coupled together, as is schematically shownin FIG. 9. Thus, in the case of FIG. 6 it is possible to use thediaphragm 18 to introduce into the electrical means the factor of filmspeed. In the case of FIG. 5, however, the

diaphragm 18 is coupled with the diaphragm 20 so as to be adjustedsimultaneously therewith. Thus, the diaphragm 18 of FIG. will influencethe external photosensitive means 4 according to the size of theexposure aperture. In the case where the diaphragm 18 is used for filmspeed, as indicated in FIG. 6, the transmission from the diaphragm iscoupled additionally to the emitter resistor 12 of thetrigger-transistor means 10 to adjust the resistor 12 according to theexposure aperture set by the diaphragm 20.

The above-described structure operates as follows:

Referring to FIG. 1 where the basic arrangement of the invention isillustrated, the potentiometer 12 is initially adjusted according to thespeed of the film which is exposed, or it may be adjusted according tothe size of the exposure aperture which is set into the camera with thediaphragm thereof. Then the main switch 17 is closed so that thecircuits will be supplied from the battery 3, and the operator directsthe camera toward the well known, the speed with which the voltage risesacross the terminals of the capacitor 9 is determined by the intensityof the photocurrent, and accordingly by the resistance resulting in thephotosensitive resistor 4 from the light which has been receivedthereby. Thus,

, the brightness of the object which is to be photogobject which is tobe photographed. The light from the object which travels through theobjective, and which is the same light that reaches the film duringexposure, is received by the internal photosensitive means 1, whileexternal light is received by the external photosensitive means 4, inthe manner described above and shown schematically in FIG. 7.

At this time the camera is in a condition preparatory to making anexposure. In this condition the switch 5 is in its normal positionengaging the contact a. Also, at this time the double-throw switch 8 isin its normal position engaging the contact X and Y as is also indicatedin FIG. 7. Thus, it will be seen that at this time the electrical meansof the invention places the capacitor 7 between the pair ofphotosensitive means 1 and 4, and of course at this time thepre-adjusted resistors 2 and 6 are also in the circuit. Therefore, therewill be at this time across the terminals of the capacitor 7 the voltagewhich is applied across the points X and Y and this latter voltage is ofcourse under the influence of the value of the resistance variation inaccordance with the intensity of the light received by thephotosensitive resistors 1 and 4. Because of the fact that the objectivewill provide a somewhat greater light loss than the window 36 throughwhich the light reaches the photosensitive means 4, the voltage at pointX will be somewhat lower than the voltage at junction Y,.

During the operations in connection with making an exposure, theoperator will depress the plunger or button 40, and it will be notedthat before the cam 48 can reach the switch 5 the cam 46 will reach theswitch 8, so that during the first stage of depression of theshutter-actuating means 40 it is the double-throw switch 8 which isactuated so as to be displaced away from the contacts X and Y and intoengagement with the contacts X and Y After this change-over of theposition of the switch 8, the continued downward movement of the plungeror shutter-actuating means 40 will bring about actuation of the switch 5by the cam 48 and simultaneous engagement of the tripping lever 42 ofthe shutter 44-. Thus, at the moment when the shutter is released theswitch 5 will engage the contact b. Therefore, a current controlled bythe light which is received by the external photosensitive means 4 willflow to the timing capacitor 9, so that the voltage across the terminalsthereof will rise with time. As is raphed has been sensed by thephotosensitive means 4.

As a result of the change-over of the position of the switch 8, the baseinput of the current-controlling transistor means 11 which is the highinput impedance transistor is biased through the voltage across theterminals of the capacitor 7 and controls the output currentaccordingly. Therefore, the emitter voltage E, of the trigger transistormeans 10 is determined by the adjusted resistance value of thepotentiometer 12 inserted in series in the current-control circuit ofthe transistor means 11. The triggering operation point of the triggertransistor means 10 with respect to the voltage rising across theterminals of the timing capacitor 9 is determined by this emittervoltage E The trigger transistor means 10 becomes conductive when therising voltage across the terminals of the timing capacitor 9 reachesthe trigger operation point, as determined by the emitter voltage, andthus by the magnitude of the diiferential between the light intensitiesreceived by the external photosensitive means 4 and the internalphotosensitive means 1, this differential being temporarily stored ormemorized by the capacitor 7. Of course the light received by thephotosensitive means 1 is in fact thevery same light which reaches thefilm during exposure thereof. At this instant, which is to say when thetrigger transistor means becomes conductive, the switching transistormeans 14, to the base of which is applied the voltage at the junction ofthe collector of transistor means 10 and the collector resistor 13,changes over to its non-conductive state from its conductive state, sothat the electromagnet 16, which previously prevented the shutter fromclosing because of the energizing current reaching the electromagneticmeans 16 through the conductive transistor 14, now becomes unenergizedand the shutter closes.

Therefore, according to the basic operation which is achieved with thepresent invention, the bias voltage of the switching transistor means 14is automatically regulated by a compensation signal for the signal whichis received by the external photosensitive means 4. Of course, thiscompensation signal is obtained by way of the internal photosensitivemeans 1. A proper exposure is achieved with this compensation of theinvention as a result of the automatic variation of the triggeringvoltage level relative to the rising voltage across the terminals of thetiming capacitor 9, based upon the illumination signal achieved from theexternal photosensiwhich is exposed or in accordance with the exposureaperture which is set into the camera at the objective thereof. Thus,the light which is received by the photosensitive means 4 will in thisway be influenced in accordance with one of these exposure-determiningfactors. Therefore, with this latter factor thus being introduced intothe operation, the signal received from the photosensitive means 4 willtake into account not only the illumination of the object which is to bephotographed but also the particular exposure-determining factor whetherit be the speed of the film or size of the exposure aperture. Coupledwith the adjustable diaphragm 18 is the potentiometer 2 which replacesthe adjustable resistor 2 shown in FIG. 1. It is this potentiometer 2which is in series with the photosensitive means 1, and the adjustmentsimultaneously with the diaphragm 18 brings about a compensation signal,temporarily memorized by the capacitor 7, which corresponds only to thedifference between the light received by the photosensitive means 1, onthe one hand, and the photosensitive means 4, on the other hand. Inother words by coupling the adjustment of the potentiometer 2' to theadjustment of the diaphragm 18, the influence on the differentialrecorded at the capacitor 7 by the diaphragm 18 is eliminated.

Therefore, with the embodiment of FIG. 2 also, the compensating signalderived from the photosensitive means 1 will assure a proper exposuretime in response to the level of the triggering voltage. Thus, anaccurate precise exposure is assured. In the event that the fixedresistor 12' of FIG. 2 is replaced by a variable resistor such as apotentiometer 12 as illustrated in FIG. 1, adjusted either according tofilm speed or exposure aperture, whichever one is not set into thecamera by way of the diaphragm 18, then the exposure time controloperations will be carried out taking into account these twoexposure-determining factors.

Referring now to FIG. 3, it will be noted from the above descriptionthat in this case the current-controlling transistor means formed by thehigh input impedance transistor 11 is inserted between the externalphotosensitive means 4 and the timing capacitor 9, and of course thetransistor means 11 is the one which is under the control of thecapacitor 7 which temporarily memorizes, in the form of the voltageacross its terminals, the differential between the light received by thephotosensitive means 1 and the light received by the photosensitivemeans 4, as mentioned above. Thus, the current flowing to the timingcapacitor 9 is controlled not only by the external photosensitive means4 but also by the current controlling transistor means 11 and thuscorresponds to the illumination at the external photosensitive means 4,compensated by the illumination at the internal photosensitive means 1.Therefore, in this example the time required for the rise of the voltageacross the terminals of the timing capacitor9 is determined according toan illumination signal which is compensated before it reaches the timingcapacitor 9. Of course the value of the voltage across the terminals ofthe timing capacitor 9 will bring about the triggering of the transistor10. The transistor will then bring about the change-over of thetransistor 14 from its nonblocking to its blocking or non-conductivecondition, so that the instant when the electromagnetic means 16 becomesunenergized is brought about with an exposure time which takes intoaccount the light actually received by the film itself. In this way thisembodiment also will achieve an extremely accurate exposure time.

With the embodiment of FIG. 4 the current-controlling transistor means 11 is in the circuit between the capacitor 7 and the meter 19 whichthrough a suitable transmission drives the adjustable means forming thediaphragm 18. Thus, in this case the timing capacitor 9 will receivecurrent, as regulated by the photosensitive resistor 4, which hasalready been compensated by the signal from the capacitor 7. Thus, inthis case the compensation signal is used to adjust the diaphragm 18 sothat the control of the amount of light reaching the photosensitivemeans 4 is directly compensated with the embodiment of FIG. 4. In thisway also an extremely accurate exposure time control is achieved, as wasthe case with the above embodiments.

Referring to FIG. 5, the objective diaphragm 20 is adjusted to determinethe exposure aperture. Thus, the light which reaches the internalphotosensitive means l is influenced by this adjustment. Therefore, thelight from the object which is received by the photosensitive means 1 isinfluenced by the size of the exposure aperture. The aperture of thediaphragm 18 which is in front of the photosensitive means 4 isautomatically adjusted by a mechanical coupling with the diaphragm 20 sothat the amount of light which reaches the photosensitive means 4 isrestricted or influenced in precisely the same way as the light whichreaches the photosensitive means 1. This mechanical coupling isillustrated in FIG. 9, where, for example, the rotary ringsof thediaphragms l8 and 20 form a pair of meshing gears. Thus, the pair ofphotosensitive means 1 and 4 are in this case influenced by the sameapertures. These diaphragms 20 and 18 are also mechanically coupled withthe variable resistors 2 and 6 so that the latter are alsosimultaneously adjusted, these resistors of course being in series withthe pair of photosensitive means I and 4, respectively. With thisoperation the arrangement is such that the resistance variation is in ageometric progression with a common ratio 2, and the apertures providedby the pair of diaphragms 20 and 18 will result in incrementalvariations of the pair of photosensitive means 1 and 4. Incorrespondence with these incremental variations there are incrementalvariations of the values of the variable resistors 2' and 6. As a resultthe voltage at point X,, as determined by the resistance of thephotosensitive resistor l and the variable resistor 2', and the voltageat the point Y as determined by the resistance of the photosensitiveresistor 4 and the variable resistor 6', correspond only to theintensity of the illumination sensed by the pair of photosensitive means1 and 4. Accordingly, the signal which is temporarily memorized andstored in the capacitor 7 is the signal of the error between theinternally light-receiving type and externally light-receiving type ofstructure, as was the case with the embodiment of FIG. 1. Thus, in theexample of FIG. 5 also an extremely precise and fully accurate exposuretime control is achieved with the signal which is derived from thecapacitor 7 serving as the compensating signal. Since in this case theresistance of the external photosensitive resistor 4 is controlled bythe adjustment of the diaphragm 18, the control of the charging currentof the timing capacitor 9 results in this timing operation being carriedout with this additional condition of the aperture magnitude which isregulated by the diaphragm l8.

, i In the case of FIG. 6, there is an objective diaphragm 20 in thesame way as in FIG. 5. However, in this case this diaphragm is notcoupled with the diaphragm 18 which is in front of the photosensitivemeans 4. Thus, this type of construction is schematically illustrated inFIG. 10. However, with FIG. 6 the adjustment of the control derived fromthe external photosensitive means 4 is made by adjustment of thetriggering voltage level of the trigger transistor means 10 in relationto the timing capacitor 9, as was the case with the above embodiments,except that in this case this control is further influenced by thesetting of the diaphragm 18 independently of the setting of thediaphragm 20. Therefore, with the embodiment of FIG. 6 it is possible tointroduce into the operation by way of the diaphragm 18, either theexposure-determining factor of the size of the exposure aperture or theexposure-determining factor of the film speed.

It will thus be seen that with the invention both an internalphotosensitive means and an external photosensitive means aresimultaneously directed toward the object which is to be photographed.The signal corresponding to the difference between the illuminationsreceived by the pair of photosensitive means, or in other words thedifference between the light received by the internal photosensitivemeans 1 and the light received by the external photosensitive means 4,is used to provide the compensating signal for correcting the timingoperation derived from the light received by the external photosensitivemeans 4 with which the relatively simple circuitry described above isconnected for achieving the automatic exposure time. It is accordinglypossible with the invention to combine the advantageous functions of theinternal photosensitive means with the advantages resulting from thesimplicity of the structure associated with the external photosensitivemeans. Therefore, it is possible to arrive at a fully accurate exposuretime with the high degree of accuracy resulting from an internalphotosensitive means while maintaining the simplicity of the structureresulting from the use of an external photosensitive means. It isfurthermore to be noted that with the invention it is possible to carryout the automatic exposure time operations while taking into accountsuch additional exposure-determining factors as the size of the exposureaperture or the speed of the film, so that the controls are carried outnot necessarily exclusively in connection with the illuminatingconditions.

What is claimed:

1. In a camera, an objective, external photosensitive means forreceiving light which is external to said objective, electrical meanselectrically connected with said external photosensitive means forautomatically determining exposure time at least partly according to thelight received by said external photosensitive means, actuation of saidelectrical means by said external photosensitive means alone havinginherent inaccuracies due to the difference between light received bysaid external photosensitive means and light which has passed throughsaid objective as well as the difference, if any, between the imageangle of said external photosensitive means and the image angle of saidobjective, and internal photosensitive means for receiving the lightwhich has passed through the objective internally thereof, said internalphotosensitive means being electrically connected with said electricalmeans for providing a compensating signal which compensates at leastpartly for said inaccuracies inherent in actuation of said electricalmeans by said external photosensitive means alone.

2. The combination of claim 1 and wherein said electrical means includesa capacitor electrically connected between said external and internalphotosensitive means for introducing into said electrical means thedifference between the light received by said external photosensitivemeans and the light received by said internal sensitive means.

- 3. The combination of claim 2 and wherein said electrical meansincludes a capacitor switch electrically connected with said capacitorand a control switch electrically connected with said externalphotosensitive means, said capacitor switch and control switch normallybeing connected in series between said external and internalphotosensitive means for normally maintaining said capacitor in aposition for receiving a signal corresponding to the difference betweenthe light received by said external and internal photosensitive means,and shutter-actuating means and a camera shutter to be actuated thereby,said shutter-actuating means coacting with said capacitor and controlswitches for first actuating said capacitor switch to disconnect saidcapacitor from said external and internal photosensitive means andconnect it, to the remainder of said electrical means and for thenactuating said control switch to connect said external photosensitivemeans to the remainder of said electrical means, said shutter-actuatingmeans actuating said camera shutter simultaneously with actuation ofsaid control switch.

4. The combination of claim 3 and wherein said electrical means includesa timing capacitor connected with said external photosensitive meanswhen said control switch is actuated by said shutter-actuating meanssimultaneously with the camera shutter, current-control transistor meansconnected electrically with said first-mentioned capacitor when saidcapacitor switch is actuated by said shutter-actuating means, triggertransistor means connected electrically with said timing capacitor andcurrent-control transistor means for providing a trigger signalaccording to the timing capacitor as influenced by said externalphotosensitive means, and said current-control transistor means, asinfluenced by the differential stored in said first-mentioned capacitor,electromagnetic means for maintaining the shutter open as long as saidelectromagnetic means is energized, and switching transistor means 5.The combination of claim 4 and wherein a potentiometer is situated insaid electrical means between said currentocontrol transistor means andsaid triggertransistor means for introducing into the electrical meansan exposure-determining factor different from exposure time.

6. The combination of claim 4 and wherein said trigger-transistor meansis electrically connected directly with said external photosensitivemeans in parallel with said timing capacitor by said control switch whenthe latter is actuated by said shutter-actuating means.

7. The combination of claim 4 and wherein said current-controltransistor means is electrically connected directly with said externalphotosensitive means by said control switch when the latter is actuatedby said shutter-actuating means.

8. The combination of claim 4 and wherein an adjustable diaphragm issituated in the path of light received by said external photosensitivemeans for influencing the amount of light received thereby, and metermeans electrically connected between said current-control transistormeans and said adjustable diaphragm for automatically adjusting thelatter according to a signal received from said current-controltransistor means as influenced by said first-mentioned capacitor, toinfluence the amount of light received by said external photosensitivemeans in accordance with a compensating signal determined by the lightreceived by said internal photosensitive means.

9. The combination of claim 1 and wherein an adjustable means coactswith said external photosensitive means for influencing the lightreceived thereby according to an exposure-determining factor difi'erentfrom exposure time, and a variable resistor means fon'ning part of saidelectrical means and connected with said adjustable means to be adjustedsimultaneously therewith for eliminating from said electrical means afalse influence which otherwise would be introduced by actuation of saidadjustable means.

10. The combination of claim 9 and wherein said adjustable means is adiaphragm, and a second diaphragm coacting with the objective fordetermining the exposure aperture, said second diaphragm beingelectrically connected with the diaphragm which forms an adjustablemeans to bring about simultaneous adjustment of both diaphragms, andsaid electrical means including a second variable resistor meanselectrically connected with said second diaphragm to be actuatedsimultaneously therewith for eliminating a false influence whichotherwise might be introduced by actuation of said second diaphragm.

11. The combination of claim 9 and wherein a diaphragm coacts with saidobjective for setting the exposure aperture, said electrical meansincluding a pair of variable resistors both actuated simultaneously withsaid diaphragm for adjusting the electrical means according to thesetting of said diaphragm, and a third variable resistor, actuated bysaid adjustable means which coacts with said external photosensitivemeans.

1. In a camera, an objective, external photosensitive means for receiving light which is external to said objective, electrical means electrically connected with said external photosensitive means for automatically determining exposure time at least partly according to the light received by said external photosensitive means, actuation of said electrical means by said external photosensitive means alone having inherent inaccuracies due to the difference between light received by said external photosensitive means and light which has passed through said objective as well as the difference, if any, between the image angle of said external photosensitive means and the image angle of said objective, and internal photosensitive means for receiving the light which has passed through the objective internally thereof, said internal photosensitive means being electrically connected with said electrical means for providing a compensating signal which compensates at least partly for said inaccuracies inherent in actuation of said electrical means by said external photosensitive means alone.
 2. The combination of claim 1 and wherein said electrical means includes a capacitor electrically connected between said external and internal photosensitive means for introducing into said electrical means the difference between the light received by said external photosensitive means and the light received by said internal sensitive means.
 3. The combination of claim 2 and wherein said electrical means includes a capacitor switch electrically connected with said capacitor and a control switch electrically connected with said external photosensitive means, said capacitor switch and Control switch normally being connected in series between said external and internal photosensitive means for normally maintaining said capacitor in a position for receiving a signal corresponding to the difference between the light received by said external and internal photosensitive means, and shutter-actuating means and a camera shutter to be actuated thereby, said shutter-actuating means coacting with said capacitor and control switches for first actuating said capacitor switch to disconnect said capacitor from said external and internal photosensitive means and connect it, to the remainder of said electrical means and for then actuating said control switch to connect said external photosensitive means to the remainder of said electrical means, said shutter-actuating means actuating said camera shutter simultaneously with actuation of said control switch.
 4. The combination of claim 3 and wherein said electrical means includes a timing capacitor connected with said external photosensitive means when said control switch is actuated by said shutter-actuating means simultaneously with the camera shutter, current-control transistor means connected electrically with said first-mentioned capacitor when said capacitor switch is actuated by said shutter-actuating means, trigger transistor means connected electrically with said timing capacitor and current-control transistor means for providing a trigger signal according to the timing capacitor as influenced by said external photosensitive means, and said current-control transistor means, as influenced by the differential stored in said first-mentioned capacitor, electromagnetic means for maintaining the shutter open as long as said electromagnetic means is energized, and switching transistor means connected with said electromagnetic means for maintaining the latter energized as long as said switching transistor means remains conductive, said switching transistor means being operatively connected to said trigger-transistor means to be rendered non-conductive in response to a trigger signal from said trigger-transistor means, so that when said switching transistor means becomes non-conductive said electromagnetic means becomes unenergized and the shutter closes to terminate the exposure.
 5. The combination of claim 4 and wherein a potentiometer is situated in said electrical means between said current-control transistor means and said trigger-transistor means for introducing into the electrical means an exposure-determining factor different from exposure time.
 6. The combination of claim 4 and wherein said trigger-transistor means is electrically connected directly with said external photosensitive means in parallel with said timing capacitor by said control switch when the latter is actuated by said shutter-actuating means.
 7. The combination of claim 4 and wherein said current-control transistor means is electrically connected directly with said external photosensitive means by said control switch when the latter is actuated by said shutter-actuating means.
 8. The combination of claim 4 and wherein an adjustable diaphragm is situated in the path of light received by said external photosensitive means for influencing the amount of light received thereby, and meter means electrically connected between said current-control transistor means and said adjustable diaphragm for automatically adjusting the latter according to a signal received from said current-control transistor means as influenced by said first-mentioned capacitor, to influence the amount of light received by said external photosensitive means in accordance with a compensating signal determined by the light received by said internal photosensitive means.
 9. The combination of claim 1 and wherein an adjustable means coacts with said external photosensitive means for influencing the light received thereby according to an exposure-determining factor different from exposure time, and a variable resistor means forming part of said electrical means and conNected with said adjustable means to be adjusted simultaneously therewith for eliminating from said electrical means a false influence which otherwise would be introduced by actuation of said adjustable means.
 10. The combination of claim 9 and wherein said adjustable means is a diaphragm, and a second diaphragm coacting with the objective for determining the exposure aperture, said second diaphragm being electrically connected with the diaphragm which forms an adjustable means to bring about simultaneous adjustment of both diaphragms, and said electrical means including a second variable resistor means electrically connected with said second diaphragm to be actuated simultaneously therewith for eliminating a false influence which otherwise might be introduced by actuation of said second diaphragm.
 11. The combination of claim 9 and wherein a diaphragm coacts with said objective for setting the exposure aperture, said electrical means including a pair of variable resistors both actuated simultaneously with said diaphragm for adjusting the electrical means according to the setting of said diaphragm, and a third variable resistor actuated by said adjustable means which coacts with said external photosensitive means. 